Petroleum fuels such as residual fuel oils and gas turbine fuels contain vanadium contaminants. These contaminants caused corrosion in the engine or turbine blades. The art recognized that by adding relatively large amounts of magnesium, the magnesium would apparently complex the vanadium and reduce corrosion. It was known to add magnesium, as magnesium sulfate (epsom salt), magnesium acetate, magnesium chloride, magnesium oxide or magnesium carbonate to gas turbine fuels containing vanadium to reduce the corrosion in the turbine blades. One such process is disclosed in U.S. Pat. No. 3,994,699, granted Nov. 30, 1966, to Scott.
Another approach was to add a slurry or paint-like suspension containing substantial amounts of magnesium oxide. The suspension desirably contained 25 to 30% by weight of magnesium, but this paint-like suspension required specialized handling and injection equipment to maintain the magnesium oxide in suspension.
A more recent approach to reducing vanadium corrosion is disclosed in U.S. Pat. No. 5,561,977, granted Oct. 8, 1996, to Harada et al. ("Harada"). Harada disclosed the controlled step-wise addition of metal oxides, e.g., MgO, with initial Mg/V ratios of 2 to 5, in a predetermined cycle of turbine operations.
It was also known in the fuel art to use a magnesium-alkoxide-carbonate complex in combination with an oil soluble sulfonate and a carboxylate and/or phenate dispersing agent as a fuel additive for reducing sediment in vanadium-containing fuels, such as is disclosed in U.S. Pat. No. 4,056,479, granted Nov. 1, 1977, to Redmore et al. ("Redmore"). While the Redmore additives had a magnesium content of about 12.5% to about 14.6%, they generally had undesirable high viscosities.
The fuel art was thus directed to an increased magnesium content additive with practical viscosities.
One attempt to achieve this was to modify the process disclosed in U.S. Pat. No. 4,129,589, granted Dec. 12, 1978, to Eliades et al. ("Eliades"). Eliades disclosed a process for preparing overbased magnesium sulfonate detergents using a promoter system comprised of a lower carboxylic acid, particularly acetic acid, water, and optionally a lower alkanol. The overbased products disclosed in Eliades generally contained only about 9% to 10% by weight of magnesium but were successful detergents for lubrication or engine oils. With controlled or tailored process parameters, the Eliades process produced an overbased product having upwards to no more than about 14% by weight of magnesium with a viscosity below about 200 cSt at 100.degree. C. The Eliades increased magnesium content product had practical viscosities, and achieved acceptance as a fuel oil additive.
Heretofore it was recognized that treating a low (up to about 1% by weight) asphaltene, low aromatic hydrocarbon liquid with an overbased magnesium sulfonate reduced limited asphaltene fouling. This treatment is disclosed in U.S. Pat. No. 4,931,164, granted Jun. 5, 1990 to Dickakian.
More recently it was found that fuel oils, such as residual fuel oils, which contained both high asphaltenes (at least more than 1%, and generally at least 3 to 4% by weight) and highly overbased magnesium sulfonates would, under adverse storage conditions, particularly with water present, produced deposits or sediment containing both magnesium and asphaltenes. This magnesium/asphaltene deposit or sediment plugged the fuel filters. That is, the addition of increased magnesium, while addressing the vanadium corrosion problem, would in combination with high amounts of asphaltenes, cause extensive deposit or sediment.
The fuel art was then faced with the predicament of producing higher magnesium content additives to reduce vanadium contaminant corrosion in the turbine, while where high asphaltenes are present, nonetheless also reduce high magnesium/asphaltene sediment which plugged filters upstream of the turbine.
The fuel art thus desired a high magnesium (i.e., in excess of 14% by weight) additive for a residual fuel oil which reduced, if not eliminated, high magnesium/asphaltene sediment with consequential filter plugging, and yet such high magnesium additive would nonetheless have practical viscosities precluding specialized handling, while also being cost effective.